Astronomy & Astrophysics manuscript no. coralieXV˙EccentricPlanets-astroph c ESO 2018 December 2, 2018

The CORALIE survey for southern extra-solar planets XV. Discovery of two eccentric planets orbiting HD 4113 and HD 156846. ?

O. Tamuz1,2, D. Segransan´ 1, S. Udry1, M. Mayor1, A. Eggenberger3,1, D. Naef4, F. Pepe1, D. Queloz1, N.C. Santos5, B.-O. Demory1, P. Figuera1, M. Marmier1, and G. Montagnier1,3

1 Observatoire astronomique de l’Universite´ de Geneve,` 51 ch. des Maillettes - Sauverny -, CH-1290 Versoix, Switzerland 2 School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv, Israel 3 Laboratoire d’Astrophysique de Grenoble, BP 53, 38041 Grenoble Cedex 4 European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Santiago 19, Chile 5 Centro de Astrof´ısica , Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal

Received/accepted

ABSTRACT

We report the detection of two very eccentric planets orbiting HD 4113 and HD 156846 with the CORALIE Echelle spectrograph mounted on the 1.2-m Euler Swiss telescope at La Silla. The first planet, HD 4113 b, has minimum of m sin i = 1.6 ± 0.2 MJup, a period of P = 526.59 ± 0.21 days and an eccentricity of e = 0.903 ± 0.02. It orbits a metal rich G5V at a = 1.28 AU which displays an additional drift of 28 m s−1/yr observed during 8 . The combination of the radial-velocity data and the non-detection of any stellar companion in our high contrast images taken at the VLT with NACO/SDI, characterizes the companion as a probable or as a faint white dwarf. The second planet, HD 156846 b, has of m sin i = 10.45 ± 0.05 MJup, a period of P = 359.51 ± 0.09 days, an eccentricity of e = 0.847 ± 0.002 and is located at a = 1.0 AU from its parent star. HD 156846 is a metal rich G0 dwarf and is also the primary of a wide binary system (a > 250 AU, P > 4000 years). Its stellar companion, IDS 17147-1914 B , is a M4 dwarf. The very high eccentricities of both planets can be explained by Kozai oscillations induced by the presence of a third object. Key words. : planetary systems — Stars: binaries: visual — Techniques: radial velocities — Stars: individual: HD 4113 — Stars: individual: HD 156846

1. Introduction therein for reviews on different aspects of the orbital-element distributions or primary star properties). The CORALIE radial-velocity planet-search programme has been In this paper we report the detection of two of the most ec- on-going for more than 9 years (since June 1998) at the 1.2- centric known planets , HD 4113 b and HD 156846 b. Together meter Swiss telescope located at La Silla Observatory, Chile. It with HD 80606 b (Naef et al. 2001) and HD 20782 b (Jones et al. is a volume-limited planet-search survey that contains all main 2006), only four of the known planets have eccentricities larger sequence stars from F8 down to K0 within 50 pc and has a color- than 0.8. The possible origin of these eccentricitie is still under dependant distance limit for later type stars down to M0 (Udry debate. Suggestions have been made for scenarios which allow et al. 2000). Among the 1650 stars surveyed, 40 percent of them −1 the formation of eccentric orbits in a protoplanetary disk of plan- have a radial-velocity accuracy of 5 m s or better and 90 per- etesimals (Levison et al. 1998) or gas (Goldreich & Sari 2003). cent of the sample is monitored with an accuracy better than 10 −1 However, the presence of the third body in both HD 156846 b m s , the limitation being mainly due to photon noise. The re- and HD 4113 b suggests that eccentricity pumping might be at maining 10 percent of the sample have a lower accuracy due to work in those two cases (Kozai 1962; Holman et al. 1997; the lower signal to noise ratio and/or to the fast rotation of the Innanen et al. 1997; Mazeh et al. 1997). targets. The paper is organized as follows. In Sect. 2 we briefly dis- arXiv:0710.5028v1 [astro-ph] 26 Oct 2007 So far, CORALIE has allowed the detection (or has con- cuss the primary star properties. Radial-velocity measurements tributed to the detection) of 48 extra-solar planet candidates and orbital solutions are presented in Sect. 3. In Sect. 4, we pro- (e.g. Mayor et al. 2004; Segransan´ et al. 2007). This substantial vide some concluding remarks. contribution together with discoveries from various other pro- grammes have provided a sample of more than 230 that now permits us to point out interesting statistical constraints 2. Stellar characteristics for the planet formation and evolution scenarios (see e.g. Marcy et al. 2005; Udry et al. 2007; Udry & Santos 2007), and reference 2.1. HD 4113, (HIP 3391, SAO 192693)

Send offprint requests to: Damien Segransan,´ e-mail: HD 4113 is identified as a G5 dwarf in the Hipparcos cata- [email protected] log (ESA 1997) and has an astrometric parallax, π = 22.70 ± ? Based on observations collected with the CORALIE echelle spec- 0.99 mas which sets the star at a distance of 44.0 pc from the trograph on the 1.2-m Euler Swiss telescope at La Silla Observatory, . With an V = 7.88 this implies an ab- ESO, Chile solute magnitude of MV = 4.66. According to the Hipparcos 2 O. Tamuz et al.: The CORALIE survey for southern extra-solar planets

Table 1. Observed and inferred stellar parameters for the stars hosting translates into an estimated binary semimajor axis of 315 AU, us- planets presented in this paper. Definitions and sources of the quoted ing the statistical relation a/r = 1.261 (Fischer & Marcy 1992). values are given in the text.

Parameters HD 4113 HD 156846 3. radial-velocity measurements and orbital Spectral Type G5V G0V V 7.88 6.506 solutions B − V 0.716 0.557 3.1. HD 4113 π [mas] 22.70 ±0.99 20.41±0.93 MV 4.660 3.055 We took 130 spectra of HD4113 from October 1999 to October Teff [K] 5688±26 6138±36 2007, yielding radial-velocity measurements with a typical log g [cgs] 4.40±0.05 4.15±0.10 signal-to-noise ratio of 50 (per pixel at 550 nm) with precision [Fe/H] [dex] 0.20±0.04 0.22±0.05 of ∼ 3.5 m s−1. L [L ] 1.22 4.98 Figure 1 shows the CORALIE radial velocities and the cor- M? [M ] 0.99 1.43 v sin i [km s−1] 1.37 4.45 responding best-fit Keplerian model with a linear drift. The re- Age [Gyr] 4.8-8.0 2.1-2.7 sulting orbital parameters are P = 526.58 days, e = 0.90, K = 97.7 m s−1, imply the presence of a planet of minimum mass m sin i = 1.63 MJup orbiting with a semi-major axis a = 1.28 AU. catalogue the for HD 4113 is B − V = 0.716. Using a The orbital separation ranges from 0.12 AU at periastron to bolometric correction BC = −0.136 (Flower 1996) and the solar 2.4 AU at apoastron. Residuals are somewhat larger than the pre- −1 Mbol = 4.746 (Lejeune et al. 1998), we thus cision of the measurements (σ(O−C) = 8.4 m s ), and are proba- obtain a L = 1.22 L . Stellar parameters for HD 4113 bly caused by a combination of stellar jitter and the inadequate are summarized in Table 1. modeling of the long period companion. A detailed spectroscopic analysis of HD 4113 was performed In addition to the Keplerian signal, the radial-velocity mea- − − using high signal to noise CORALIE spectra in order to obtain ac- surements display a 28 m s 1 yr 1 linear drift with a curvature curate atmospheric parameters (see Santos et al. 2005, for further of over -1.55 m s−1 yr−2 over a time span of 8 years induced details). This gave the following values: an effective temperature by a companion at a larger separation. Based on the duration Teff = 5688 ± 26 K, a log g = 4.4 ± 0.05, and a and the amplitude of the drift, we are able to make some [Fe/H] = 0.20 ± 0.04. Using these parameters and estimates on the nature of the outer companion of HD 4113. the Geneva models (Meynet & Maeder 2000), The lowest possible companion mass responsible for the drift we derive a mass M = 0.99 M . According to the Bayesian has m sin i = 10 MJup which correspond to an age estimates of Pont & Eyer (2004), HD 4113 is an old main- of 11.5 , an eccentricity of e = 0.5 and a radial-velocity − sequence star (4.8-8.0 Gyr). From the CORALIE spectra we de- semi-amplitude of 150 m s 1. However, this orbital solution rive v sin i = 1.37 km s−1 (Santos et al. 2002). is very unlikely since the outer planet-star separation would reach 2.5 AU at periastron which is the separation of the inner planet at apoastron. More realistic solutions therefore have 2.2. HD 156846 (HIP 84856 , HR 6441, IDS 17147-1914 A) longer periods. For instance, the shortest orbital period for a HD 156846 is a bright, metal-rich and slightly evolved G0 dwarf. circular orbit is 22 years and correspond to a probable brown The astrometric parallax from the Hipparcos catalogue, π = dwarf companion ( m sin i = 14 MJup) orbiting HD 4113 at 20.41 ± 0.93 mas (ESA 1997) sets the star at a distance of a = 7.9 AU. The companion would reach the hydrogen burning 49.0 pc from the Sun. With an apparent magnitude V = 6.50 limit at a separation of 20 AU with a period of 90 years. Radial velocities allow to conclude that the companion responsible this implies an absolute magnitude of MV = 3.055. According to the Hipparcos catalogue the color index for HD 156846 is for the observed drift is unlikely to be a planet (orbit stability B − V = 0.578. Using the method described in the previous reasons) but cannot discriminate between a brown dwarf and a stellar companion. section we derive a luminosity L = 4.98 L with a bolometric correction of BC = −0.049. Stellar parameters for HD 156846 are summarized in Table 1 as well. To bring additional constraints on the outer companion’s na- A detailed spectroscopic analysis of HD 156846 gave the fol- ture we obtained high contrast images of the target using the VLT and its adaptive optics system NACO in differential mode lowing values: an effective temperature Teff = 6138 ± 36 K, a surface gravity log g = 4.15 ± 0.10, and a metallicity [Fe/H] = (Montagnier et al. 2007). We did not detect any object within 0.22 ± 0.05. Using these parameters and the Geneva stellar evo- a radius of 2.5 arcsec, which excludes any main sequence stel- lution models, we deduce a mass M = 1.43 M . According to lar companions to HD 4113 down to 0.2 arcsec ( about 8 AU), the Bayesian age estimates of Pont & Eyer (2004), HD 156846 (Montagnier et al., in prep.). We conclude that the companion re- is a moderately old main-sequence star (2.1-2.7 Gyr).From the sponsible for the observed drift is likely to be either a faint white CORALIE spectra we derive v sin i = 4.45 km s−1. dwarf like GJ 86 B (Mugrauer & Neuhauser¨ 2005; Lagrange HD 156846 is the primary star of a wide binary system et al. 2006) that went undetected in our SDI images or it could (Washington Double Star catalog, hereafter WDS Worley & be a brown dwarf located between 8 and 20 AU from the parent Douglass 1996) with an angular separaion of ρ = 5.100 and a star with a period ranging from 20-90 years. position angle PA=75 deg. Based on its near infrared magnitude (J=9.405, H=8.92, ie. Cabrera-Lavers et al. 2006) and on the 3.2. HD 156846 stellar evolutionnary models of the Lyon group (Baraffe et al. 1998), its companion, IDS 17147-1914 B is identified as an early HD 156846 has been observed with CORALIE at La Silla M dwarf of mass M = 0.59M . Using the positions given in the Obervatory since May 2003. Altogether, 64 radial-velocity mea- WDS, we obtain a projected binary separation of 250 AU. This surements with a typical signal-to-noise ratio of 75 (per pixel at O. Tamuz et al.: The CORALIE survey for southern extra-solar planets 3 . . . . HD4113 CORALIE HD156846 CORALIE −67.8 5.1

−68.0 5.0 −68.2

4.9 −68.4 RV [km/s] RV [km/s]

4.8 −68.6

−68.8 40 20 20 0 0 −20 O−C [m/s] O−C [m/s] −20 −40 1500 2000 2500 3000 3500 4000 4500 2800 3000 3200 3400 3600 3800 4000 4200 4400

. JD − 2450000.0 [days] . . JD − 2450000.0 [days] . . HD4113 CORALIE . . HD156846 CORALIE .

150 600

100 400

50 200 RV [m/s] RV [m/s]

0 0

−200 −0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 −0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 φ φ . . . . Fig. 1. Radial-velocity measurements as a function of Julian Date ob- Fig. 2. Same as Fig. 1 for HD 156846. tained with CORALIE for HD 4113 superimposed on the best Keplerian planetary solution (top figure). The residuals are displayed at the bot- tom of the top figure and the phase folded radial-velocity measurements in extrasolar planets (represented in Fig. 4 as a e vs. log P di- are displayed on the bottom diagram. agram) is still under debate, and different scenario have been proposed to explain the largest eccentricities such as the Kozai oscillations (Kozai 1962), chaotic evolution of planetary orbits 550 nm) and a mean measurement uncertainty (including pho- −1 in multiple systems and formation of eccentric orbits in a pro- ton noise and calibration errors) of 2.8 m s were gathered. toplanetary disk of planetesimals (Levison et al. 1998) or gas Figure 2 shows the CORALIE radial velocities and the corre- (Goldreich & Sari 2003). sponding best-fit Keplerian model. The resulting orbital parame- HD 156846 b and HD 4113 b are two of the four most ec- ters are P = 359.50 days, e = 0.847, K = 464 m s−1 , implying a centric known planets, together with HD 80606 b (Naef et al. minimum mass m sin i = 10.45 M orbiting HD 156846 with a 2 Jup 2001) and HD 20782 b (Jones et al. 2006) with eccentricities semimajor axis a = 0.99 AU. The orbital separation ranges from larger than 0.85. It should be noticed that the parent stars of 0.15 AU at periastron to 1.8 AU at apoastron. The orbital ele- these 4 planets are part of wide binary systems (Desidera & ments for HD 156846 b are listed in Table 2. Residuals around Barbieri 2007, for HD 20782 and respective discovery papers the single planet orbital solution are larger than the precision of for HD80606, HD 4113 and HD 156846) raising the question of the measurements (σ = 7.5 m s−1) which points toward the (O−C) the influence of the third body on the planets orbital parameters. stellar jitter since the the high eccentricity of HD 156846 b does It is therefore tempting to investigate the eccentricity pumping not leave much room for a short period undetected planet. scenario a bit further by computing the different time-scales in- volved. 4. Discussion & conclusion The Kozai mechanism is effective at very long range, but its oscillations may be suppressed by other competing sources of or- In this paper, we have reported the detection of two very ec- bital perturbations, such as general relativity effects or perturba- centric planets orbiting two metal rich G dwarfs - HD 4113 and tions resulting from the presence of an additional companion in HD 156846 - for which a third massive body is present in each the system. Regarding HD 4113 and HD 156846 , we have esti- planetary system. The origin of the wide range of eccentricities mated their Kozai oscillation periods using Eqs (36) of Ford et al. 4 O. Tamuz et al.: The CORALIE survey for southern extra-solar planets

Table 2. CORALIE best Keplerian orbital solutions for HD 156846 and HD 4113, as well as inferred planetary parameters. Confidence in- tervals are computed for a 68% confidence level after 10000 montecarlo iterations. Span is the time interval in days between the first and last measurements. σ(O − C) is the weighted r.m.s. of the residuals around the derived solutions

Parameters HD 4113 HD 156846 γ [km s−1] 4.874 ± 0.05 −68.540 ± 0.001 slope [m s−1 yr−1] 27.8 ± 0.3 - curvature [m s−1 yr−2] −1.55 ± 0.17 - P [days] 526.62 ± 0.3 359.51 ± 0.09 K [m s−1] 97.1 ± 3.8 464.3 ± 3.0 e 0.903 ± 0.005 0.8472 ± 0.0016 ω [deg] −42.3 ± 1.9 52.23 ± 0.41 6 T0 [JD-2.45 10 ] 3778.0 ± 0.2 3998.09 ± 0.05 −3 a1 sin i [10 AU ] 2.01 ± 0.05 8.15 ± 0.04 f m −9 . ± . ± ( ) [10 M ] 3 9 0 3 558 9 Fig. 3. e vs. log P for the known extra-solar giant planets orbiting dwarf m i . ± . . ± . 2 sin [MJup] 1 56 0 04 10 45 0 05 primaries. Filled dots are for planets orbiting single stars and open a [AU ] 1.28 0.9930 squares for planets orbiting a component of a multiple stellar system. Nmes 130 64 Green stars correspond to stars hosting Netpune-like planets. HD 4113 b Span [years] 8.0 4.45 −1 and HD 156846 b are located by filled red squares. σ(O−C) [m s ] 8.4 7.7

Ford, E. B., Kozinsky, B., & Rasio, F. A. 2000, ApJ, 535, 385 Goldreich, P. & Sari, R. 2003, ApJ, 585, 1024 6 (2000) . This yields to PKozai = 5.5 10 years for HD 156846 and Holman, M., Touma, J., & Tremaine, S. 1997, Nature, 386, 254 3 PKozai = 6.2 10 years for HD 4113 which indicates that both Innanen, K. A., Zheng, J. Q., Mikkola, S., & Valtonen, M. J. 1997, AJ, 113, 1915 planet eccentricity can undergo Kozai oscillations with periods Jones, H. R. A., Butler, R. P., Tinney, C. G., et al. 2006, MNRAS, 369, 249 Kozai, Y. 1962, AJ, 67, 591 that are many order of magnitude shorter than the age of the Lagrange, A.-M., Beust, H., Udry, S., Chauvin, G., & Mayor, M. 2006, A&A, systems. We also computed the apsidal precession period due to 459, 955 relativistic corrections to the newtonian equation of motion us- Lejeune, T., Cuisinier, F., & Buser, R. 1998, A&AS, 130, 65 Levison, H., Lissauer, J., & Duncan, M. 1998, AJ, 116, 1998 ing Eq. (4) of Holman et al. (1997). This yields PGR = 1.1Gyr andP = 7.6Gyr for HD 156846 and for HD 4113 respectively. Marcy, G., Butler, R. P., Fischer, D., et al. 2005, Progress of Theoretical Physics GR Supplement, 158, 24 This is also several order of magnitude larger that the Kozai os- Mayor, M., Udry, S., Naef, D., et al. 2004, A&A, 415, 391 cillation period. Mazeh, T., Krymolowski, Y., & Rosenfeld, G. 1997, ApJ, 477, L103 Provided that the orbital planes of the inner planet and the Meynet, G. & Maeder, A. 2000, A&A, 361, 101 outer companion have different inclinations, the eccentricities of Montagnier, G., Segransan,´ D., Beuzit, J.-L., et al. 2007, in Proceedings of the conference In the Spirit of Bernard Lyot: The Direct Detection of Planets and both HD4113 b and HD 156846 b could undergo Kozai oscilla- Circumstellar Disks in the 21st Century. June 04 - 08, 2007. University of tions. That would be the most likely explanation for such high California, Berkeley, CA, USA. Edited by Paul Kalas., ed. P. Kalas eccentricities. Mugrauer, M. & Neuhauser,¨ R. 2005, MNRAS, 361, L15 Naef, D., Latham, D. W., Mayor, M., et al. 2001, A&A, 375, L27 Acknowledgements. We are grateful to the staff from the Geneva Observatory, Pont, F. & Eyer, L. 2004, MNRAS, 351, 487 in particular to L.Weber, for maintaining the 1.2-m Euler Swiss telescope and Santos, N., Israelian, G., Mayor, M., et al. 2005, A&A, 437, 1127 the CORALIE echelle spectrograph at La Silla, and for technical support dur- Santos, N., Mayor, M., Naef, D., et al. 2002, A&A, 392, 215 ing observations. We thank the Swiss National Research Foundation (FNRS) Segransan,´ D., Udry, S., Mayor, M., et al. 2007, A&A, to be submitted and the Geneva University for their continuous support to our planet search pro- Udry, S., Fischer, D., & Queloz, D. 2007, in Protostars and Planets V, ed. grammes. We would like to thank T. Mazeh for usefull discussions and the ref- B. Reipurth, D. Jewitt, & K. Keil, 685–699 eree for his thoughtful comments. NCS would like to thank the support from Udry, S., Mayor, M., Naef, D., et al. 2000, A&A, 356, 590 Fundac¸ao˜ para a Cienciaˆ e a Tecnologia, Portugal, in the form of a grant (refer- Udry, S. & Santos, N. C. 2007, ARA&A, 45, 397 ence POCI/CTE-AST/56453/2004), as well as support by the EC’s FP6 and by Worley, C. E. & Douglass, G. G. 1996, VizieR Online Data Catalog, 1107, 0 FCT (with POCI2010 and FEDER funds), within the HELAS international col- laboration. Support from the Fundao para Cincia e a Tecnologia (Portugal) to P. F. in the form of a scholarship (reference SFRH/BD/21502/2005) is gratefully acknowledged. A.E. acknowledges support from the Swiss National Science Foundation through a fellowship for prospective researcher. This research has made use of the VizieR catalogue access tool operated at CDS, France.

References Baraffe, I., Chabrier, G., Allard, F., & Hauschildt, P. H. 1998, A&A, 337, 403 Cabrera-Lavers, A., Garzon,´ F., Hammersley, P. L., Vicente, B., & Gonzalez-´ Fernandez,´ C. 2006, A&A, 453, 371 Desidera, S. & Barbieri, M. 2007, A&A, 462, 345 ESA. 1997, The HIPPARCOS and TYCHO catalogue, ESA-SP 1200 Fischer, D. A. & Marcy, G. W. 1992, ApJ, 396, 178 Flower, P. 1996, ApJ, 469, 355